Swollen lymph nodes usually occur as a result of exposure to bacteria or viruses. When swollen lymph nodes are caused by an infection, this is known as lymphadenitis (lim-fad-uh-NIE-tis). Rarely, swollen lymph nodes are caused by cancer.

Your lymph nodes, also called lymph glands, play a vital role in your body's ability to fight off viruses, bacteria and other causes of illnesses. Common areas where you might notice swollen lymph nodes include your neck, under your chin, in your armpits and in your groin.

In some cases, the passage of time and warm compresses may be all you need to treat swollen lymph nodes. Treatment for lymphadenitis depends on the cause.

Your lymphatic system comprises a network of organs, vessels and numerous lymph nodes situated throughout your body. Most of your lymph nodes are located in your head and neck region. Lymph nodes that frequently swell are in this area, as well as in your armpits and groin area.

Swollen lymph nodes are a sign that something is wrong somewhere in your body. When your lymph nodes first swell, you might notice:

Tender and painful lymph nodes

Swollen lymph nodes that may be the size of a pea or kidney bean, or even larger

Depending on the cause of your swollen lymph nodes, other signs and symptoms you might have include:

Runny nose, sore throat, fever and other indications of an upper respiratory infection

General swelling of lymph nodes throughout your body — which may indicate an infection, such as HIV or mononucleosis, or an immune disorder, such as lupus or rheumatoid arthritis

Are accompanied by a sore throat or by difficulty swallowing or breathing

A lymph node is a small, round or bean-shaped cluster of cells covered by a capsule of connective tissue. The cells are a combination of lymphocytes — which produce protein particles that capture invaders, such as viruses — and macrophages, which break down the captured material. Lymphocytes and macrophages filter your lymphatic fluid as it travels through your body and protect you by destroying invaders.

Lymph nodes are located in groups, and each group drains a specific area of your body. You may be more likely to notice swelling in certain areas, such as in the lymph nodes in your neck, under your chin, in your armpits and in your groin. The site of the swollen lymph nodes may help identify the underlying cause.

The most common cause of swollen lymph nodes is an infection, particularly a viral infection, such as the common cold. However, there are other types of infections, including parasitic and bacterial, and other possible causes of swollen lymph nodes. They include:

Common infections

Strep throat

Measles

Ear infections

Infected (abscessed) tooth

Mononucleosis

Skin or wound infections, such as cellulitis or erysipelas

Human immunodeficiency virus (HIV) — the virus that causes AIDS

Uncommon infections

Tuberculosis

Certain sexually transmitted infections, such as syphilis

Toxoplasmosis — a parasitic infection resulting from contact with the feces of an infected cat or eating undercooked meat

Other possible, but rare causes include certain medications, such as the anti-seizure medication phenytoin (Dilantin), and preventive medications for malaria.

If infection is the cause of your swollen lymph nodes and isn't treated, these complications might occur:

Abscess formation. An abscess is a localized collection of pus caused by an infection. Pus contains fluid, white blood cells, dead tissue and bacteria or other invaders. An abscess may require drainage and antibiotic treatment. An abscess may cause significant damage if it involves a vital organ.

Bloodstream infection (bacteremia). A bacterial infection anywhere in your body can progress to sepsis, caused by an overwhelming infection of the bloodstream. Sepsis may result in organ failure and death. Treatment involves hospitalization and intravenous antibiotics.

If you have swollen lymph nodes, you're likely to start by first seeing your family doctor. However, when you call to set up your appointment, you may be urged to seek immediate medical care if you're experiencing severe symptoms such as difficulty breathing or swallowing.

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be well prepared. Here's some information to help you get ready, and what to expect from your doctor.

What you can do

Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance.

Write down any symptoms you've been experiencing, and for how long. Among other symptoms, your doctor will want to know if you've had flu-like symptoms such as fever or sore throat, and may ask whether you've noticed changes in your weight. Include on your list every symptom, from mild to severe, that you've noticed since your lymph nodes began to swell.

Make a list of all recent exposures to possible sources of infection. These may include travel abroad, hiking in areas known to have ticks, eating undercooked meat, being scratched by a cat, or engaging in high-risk sexual behavior or sex with a new partner.

Make a list of your key medical information, including other conditions you're being treated for and the names of the medications that you're taking. Include every prescription and over-the-counter (OTC) drug you use, as well as any vitamins and supplements.

Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions can help make the most of your time together. List your questions from most important to least important in case time runs out.

I have these other health conditions. Do I need to change the treatments I've been using?

Is there a generic alternative to the medicine you're prescribing for me?

Are there any brochures or other printed material that I can take with me? What websites do you recommend?

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over points you want to discuss in-depth. Your doctor may ask:

What are your symptoms?

When did you first begin experiencing symptoms?

Have your affected lymph nodes gotten larger over time?

Are your affected lymph nodes tender?

Have you been experiencing fever or night sweats?

Have you lost weight without trying?

Do you have a sore throat or difficulty swallowing?

Have you experienced any difficulty breathing?

Have your bowel habits changed?

What medications are you currently taking?

Have you recently traveled to another country or to tick-inhabited regions? Did anyone who traveled with you get sick?

Have you recently been exposed to new animals? Were you bitten or scratched?

Have you recently had sex with a new partner?

Do you practice safe sex? Have you done so since you became sexually active?

Do you smoke? For how long?

What you can do in the meantime

While you wait for your appointment, warm compresses and OTC pain relievers, such as ibuprofen (Advil, Motrin IB, others) and acetaminophen (Tylenol, others), may make you or your child more comfortable. Don't give aspirin to your child without first consulting with your child's doctor, because of its link to the harmful Reye's syndrome.

Your medical history. In addition, your doctor will want to know when and how your swollen lymph nodes developed and if you have any other signs or symptoms.

A physical exam. Your doctor will also want to check lymph nodes near the surface of your skin for size, tenderness, warmth and texture. The site of your swollen lymph nodes and your other signs and symptoms will offer clues to the underlying cause.

Blood tests. Depending on what your doctor suspects is causing your swollen lymph nodes, certain blood tests may be done to confirm or exclude the suspected underlying condition. The specific tests will depend on the suspected cause, but most likely will include a complete blood count (CBC), which helps evaluate your overall health and detect a range of disorders, including infections and leukemia.

Imaging studies. A chest X-ray or computerized tomography (CT) scan of the affected area may help determine potential sources of infection or find tumors.

Lymph node biopsy. If your doctor can't pin down the diagnosis, it may be helpful to remove a sample from a lymph node or even an entire lymph node for microscopic examination.

The method of biopsy may be fine-needle aspiration (FNA), which your doctor may perform during an office visit, or you may be referred to a surgeon or radiologist for this procedure. In FNA, the doctor inserts a thin, hollow needle into the lymph node and removes (aspirates) cells, which are then sent to a lab for study. Ultrasound — a noninvasive procedure that uses sound waves to create images of organs and tissues — may be used to guide the needle and ensure accuracy.

In some cases, you may require an excisional biopsy. This type of biopsy — also called surgical biopsy — removes a portion or all of a lymph node through an incision for analysis. A surgeon performs this procedure while using local or general anesthetics.

Swollen lymph nodes caused by a virus may return to normal after the viral infection resolves. Antibiotics are not useful to treat viral infections. Treatment for swollen lymph nodes from other causes depends on the cause:

Infection. The most common treatment for swollen lymph nodes caused by a bacterial infection is antibiotics. If your swollen lymph nodes are due to an HIV infection, you'll receive treatment for that condition.

Immune disorder. If your swollen lymph nodes are a result of certain conditions, such as lupus or rheumatoid arthritis, treatment is directed at the underlying condition.

Cancer. Swollen nodes caused by cancer require treatment for the cancer. Depending on the type of cancer, treatment may involve surgery, radiation or chemotherapy.

If your swollen lymph nodes are tender or painful, you might get some relief by doing the following:

Apply warmth. Apply a warm, wet compress, such as a washcloth dipped in hot water and wrung out, to the affected area.

Take pain relievers. Over-the-counter pain relievers, such as aspirin, ibuprofen (Advil, Motrin IB, others) and acetaminophen (Tylenol, others), may help alleviate pain and fever. Don't give your child aspirin without consulting your doctor because of its link to Reye's syndrome in children. Reye's syndrome is a rare but serious illness that can affect the blood, liver and brain of a child or teenager recovering from a viral infection.

Get adequate rest. You often need rest to aid your recovery from the underlying condition.

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